Electrochemical cell with adjacent cathodes

ABSTRACT

The disclosure includes an electrochemical cell comprising a first cathode and a second cathodes are adjacent one another in a stacked arrangement to form a cathode stack in the electrochemical cell. The first cathode includes a first current collector and a first cathode form of active material covering the first current collector, and the second cathode includes a second current collector and a second cathode form of active material covering the second current collector. The second current collector is in electrical contact with the first current collector. The electrochemical cell further comprises an anode adjacent to the cathode stack, and a separator located between the cathode stack and the anode.

TECHNICAL FIELD

The invention generally relates to electrochemical batteries, and moreparticularly, but without limitation, to batteries for implantablemedical devices (IMDs).

BACKGROUND

Implantable medical devices (IMDs) may perform a variety of functions,including patient monitoring and therapy delivery. In general, it isdesirable to design an IMD to be as small as possible, e.g., in terms ofvolume, footprint, and/or thickness, while still effectively performingits intended function. For example, decreasing the size of an IMD canincrease the number of possible locations in which the IMD can bepractically implanted. In addition, a smaller IMD can limit theextensiveness of surgery, reduce the likelihood of infection orrejection of the implant, and improve the comfort, and in some casescosmetic appearance of a patient after implantation. In other words, asmaller IMD may be more clinically acceptable than a larger MD.

Examples of IMDs include implantable stimulators, implantable pulsegenerators (IPGs) and implantable cardioverter-delibrillators (ICDs).IPGs and ICDs comprise, among other things, a control module, acapacitor, and a battery that are housed in a hermetically sealedcontainer. IMD batteries may include includes a case, a liner, anelectrode assembly, electrolyte, and at least one feedthrough extendingthrough the case that serves as a battery terminal. The liner insulatesthe electrode assembly from the case. The electrode assembly includeselectrodes, an anode and a cathode, with a separator there between.

SUMMARY

This disclosure includes electrochemical cells such as a battery in anIMD. The battery may include multiple cathodes stacked on top of eachother. Providing multiple cathode plates increases the collectorinterfacial area. This may reduce cathode resistance. In addition,providing multiple cathode plates may also reduce in-plane expansion ofthe cathode plates during battery discharge. Finally, providing multiplecathode plates allows more shape flexibility in the thickness directionof the battery as the multiple plates may have different profiles.

In one example, this disclosure includes an electrochemical cellcomprising a first cathode and a second cathode. The first and secondcathodes are adjacent one another in a stacked arrangement to form acathode stack in the electrochemical cell. The first cathode includes afirst current collector and a first cathode form of active materialcovering the first current collector, and the second cathode includes asecond current collector and a second cathode form of active materialcovering the second current collector. The second current collector isin electrical contact with the first current collector. Theelectrochemical cell further comprises an anode adjacent to the cathodestack, and a separator located between the cathode stack and the anode.

In another example, this disclosure includes a battery comprising afirst cathode. The first cathode includes a first current collector anda first cathode form of active material covering the first currentcollector. The battery further comprises a second cathode. The secondcathode includes a second current collector and a second cathode form ofactive material covering the second current collector. The secondcurrent collector is in electrical contact with the first currentcollector. The first and second cathodes are adjacent one another in astacked arrangement to form a cathode stack in the battery. The batteryfurther comprises an anode adjacent to the cathode stack, a separatorlocated between the cathode stack and the anode, electrolyte, and abattery housing that holds the cathode stack, the anode, the separator,and the electrolyte.

In another example, this disclosure includes a method of manufacturecomprising positioning a first cathode and a second cathode adjacent oneanother in a stacked arrangement to form a cathode stack. The firstcathode includes a first current collector and a first cathode form ofactive material covering the first current collector. The second cathodeincludes a second current collector and a second cathode form of activematerial covering the second current collector. The method furthercomprises positioning an anode adjacent to the cathode stack with aseparator located between the cathode stack and the anode, andelectrically connecting the first current collector and the secondcurrent collector.

The details of one or more examples of this disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating apacemaker/cardioverter/defibrillator (PCD) with a battery including anelectrochemical cell with adjacent cathodes.

FIG. 2 is a cutaway perspective view of an implantable medical device(IMD) with a battery including an electrochemical cell with adjacentcathodes.

FIGS. 3A-3B illustrate one example of a battery including anelectrochemical cell with adjacent cathodes.

FIGS. 4-9 illustrate examples of electrochemical cells with adjacentcathodes.

FIGS. 10A-10B illustrate an example battery including an electrochemicalcell with adjacent cathodes having different lengths such that thebattery has a varying thickness.

FIG. 11 is a flow chart illustrating techniques for manufacturing abattery including an electrochemical cell with adjacent cathodes.

FIGS. 12 and 13 illustrate more examples of electrochemical cells withadjacent cathodes.

FIGS. 14 and 15 illustrate another example of an electrochemical cellwith adjacent cathodes.

FIGS. 16 and 17 illustrate another example of an electrochemical cellwith adjacent cathodes.

DETAILED DESCRIPTION

Implantable medical devices (IMDs) are used to deliver therapy topatients suffering from a variety of conditions. Examples of IMDsinclude implantable pacemakers and implantablecardioverter-defibrillators (ICDs), which are electronic medical devicesthat monitor the electrical activity of the heart and provide electricalstimulation to one or more of the heart chambers as needed. For example,a pacemaker senses an arrhythmia, i.e., a disturbance in heart rhythm,and provides appropriate electrical stimulation pulses, at a controlledrate, to selected chambers of the heart in order to correct thearrhythmia and restore the proper heart rhythm. The types of arrhythmiasthat may be detected and corrected by pacemakers include bradycardias,which are unusually slow heart rates, and certain tachycardias, whichare unusually fast heart rates.

ICDs also detect arrhythmias and provide appropriate electricalstimulation pulses to selected chambers of the heart to correct anabnormal heart rate or rhythm. In contrast to pacemakers, however, anICD can deliver cardioversion and high energy defibrillation pulses thatare mach stronger than typical pacing pulses. This is because ICDs aregenerally designed to correct fibrillation and tachycardia episodes. Tocorrect such arrhythmias, an ICD delivers a low, moderate, orhigh-energy therapy.

Pacemakers and ICDs may be designed with ergonomic shapes that arerelatively compliant with a patient's implant location and tend tominimize patient discomfort. For example, corners and edges of thedevices may have relatively generous radii to provide a device withsmoothly contoured exterior surfaces.

The electrical energy for the therapy delivered by an ICD is generatedby delivering electrical current from a power source (battery) to chargecapacitors to store energy. The capacitors are capable of rapidlydischarging, under control of a processing element, to deliver one ormore appropriate waveforms that deliver enemy via electrodes disposed incommunication with a patient's heart. In order to provide timely therapyto the patient after the detection of ventricular fibrillation, forexample, it is necessary to charge the capacitors with the requiredamount of energy as quickly as possible. Thus, the battery in an ICDmust have a high rate capability to provide the necessary current tocharge the capacitors. In addition, since ICDs are implanted inpatients, the battery must be able to accommodate physical constraintson size and shape.

It is also desirable to minimize the volume occupied by the devices.Improving the performance or charge density of batteries for IMDs,including ICD is desirable in that such improvements facilitatereductions in the size of the devices or improvements in the performanceof the devices, such as, for example, an increase in battery life.

FIG. 1 is a schematic diagram illustrating apacemaker/cardioverter/defibrillator (PCD) incorporating a battery withat least one electrochemical cell, the electrochemical cell includingadjacent cathodes. However, IMD 10 may assume a wide variety of forms.For example, IMD 10 may be an implantable cardiac defibrillator (ICD asis known in the art). Alternatively, or in addition, IMD 10 may be animplantable cardiac pacemaker.

IMD 10 includes associated electrical leads 14, 16 and 18, although itwill be appreciated that IMD 10 may include any number of leads suitablefor a particular application. Leads 14, 16 and 18 are coupled to IMD 10by via multi-port connector block 20, which contains separate ports foreach of the three leads 14, 16, and 18. Lead 14 is coupled to asubcutaneous electrode 30, which is intended to be mountedsubcutaneously in the region of the left chest. Alternatively, oradditionally, an active “can” configuration may be employed in which thehousing of IMD 10 may serve as an electrode. Lead 16 is a coronary sinuslead employing an elongated coil electrode that is located in thecoronary sinus and great vein region of a heart 12. The location of theelectrode is illustrated in broken line format at 32, and extends aroundheart 12 from a point within the opening of the coronary sinus to apoint in the vicinity of the left atrial appendage.

Lead 18 may be provided with elongated electrode coil 28, which may belocated in the right ventricle of heart 12. Lead 18 may also include ahelical stimulation electrode 34, which takes the form of an advanceablehelical coil that is screwed into the myocardial tissue of the rightventricle. Lead 18 may also include one or more additional electrodesfor near and far-field electrogram sensing.

In the system illustrated, cardiac pacing pulses are delivered betweenthe helical electrode 34 and the elongated electrode coil 28. Theelectrodes 28 and 34 are also employed to sense electrical signalsindicative of ventricular contractions. As illustrated, it isanticipated that the right ventricular electrode 28 will serve as thecommon electrode during sequential and simultaneous pulse multipleelectrode defibrillation regimens. For example, during a simultaneouspulse defibrillation regimen, pulses would simultaneously be deliveredbetween electrode 28 and electrode 30, and between electrode 28 andelectrode 32. During sequential pulse defibrillation, it is envisionedthat pulses would be delivered sequentially between subcutaneouselectrode 30 and electrode 28, and between coronary sinus electrode 32and right ventricular electrode 28. Single pulse, two electrodedefibrillation pulse regimens may also be provided, typically betweenelectrode 28 and coronary sinus electrode 32. Alternatively, singlepulses may be delivered between electrodes 28 and 30. The particularinterconnection of the electrodes to the IMD 10 will depend somewhat onwhich specific single electrode pair defibrillation pulse regimen isbelieved more likely to be employed.

As previously described, IMD 10 may assume a wide variety of forms asare known in the art. One example of various components of an IMD 100 isshown in FIG. 2. More specifically, FIG. 2 depicts an IMD 100, which maybe an implantable pulse generator (IPG, e.g., a pacemaker, or animplantable cardioverter-defibrillator (ICD, as examples. IMD 100includes a case 102, a control module 104, a battery 106 andcapacitor(s) 108. Control module 104 controls one or more sensing and/ortherapy delivery, such as stimulation therapy functions of IMD 100,which functions may be performed via leads 109. Battery 106 chargescapacitor(s) 108 and powers control module 104. Battery 106 includes anelectrochemical cell with adjacent cathodes.

FIGS. 3A-3B illustrate battery 200. More specifically, FIG. 3Aillustrates an exploded view of the components of battery 200, whereasFIG. 3B shows in the components of battery 200 in a fully-assembledconfiguration. As one example, battery 200 may be used as battery 106 inIMD 100 (FIG. 2), although battery 200 may also be used in otherapplications such as other IMDs or other devices that use batteries. Inaddition, a battery including any of the electrochemical cells disclosedherein, including any of the electrochemical cells disclosed withrespect to FIGS. 4-9, 12 and 13 may also be used as battery 106 in IMD100 (FIG. 2).

Battery 200 includes an electrochemical cell including two anodes 320A,320B (collectively “anodes 320”) and two cathodes 220A, 220B(collectively “cathodes 220”). Battery 200 further includes a two-parthousing including cup 210A and cover 210B (collectively housing “210”).Feedthrough 212 includes feedthrough pin 214 that passes through housing210 and connects to cathodes 220 to provide a positive terminal forbattery 200.

Cathodes 220 each include a current collector 222 and a cathode form 224of active material covering the current collector 222. As one example,current collector 222 may be a metallic screen formed from aluminum,stainless steel, nickel, titanium, copper an alloy thereof or othersuitable conductive material. Electrically conductive tab 223 isdirectly connected to current collector 222 and provides an electricalconnection path to current collector 222. In some examples, tab 223 maybe a unitary component with current collector 222.

The active material of cathode form 224 may comprise any cathodematerial known to those in the art. In different examples, the activematerial of cathode form 224 may include metal oxides (e.g. vanadiumoxide, silver vanadium oxide (SVO), manganese dioxide etc.), carbonmonofluoride (CFx) and hybrids thereof (e.g., CF_(x)+MnO₂), combinationsilver vanadium oxide (CSVO), lithium ion, other rechargeablechemistries, or other suitable compounds or any combination thereof.Cathode form 224 may also include binder and other inert ingredients.For example, cathode 220 may be formed by creating a mixture of activematerial powder, binder powder, solvent and then compressing the mixtureover current collector 224 or otherwise coating current collector 224with the mixture. Other techniques known to those in the art may also beused to from cathode 220.

Anodes 320 each include a current collector 322 and a form 324 of activeanode material disposed over the current collector 322. As one example,current collector 322 may be a metallic plate or foil, such as aluminum,stainless steel, nickel, titanium, copper an alloy thereof or othersuitable conductive material. Electrically conductive tab 323 isdirectly connected to current collector 322 and provides an electricalconnection path to current collector 322. In some examples, tab 323 maybe a unitary component with current collector 322. The active materialof anode form 324 may comprise any anode material known to those in theart. In one example, the active material of anode form 324 may comprisegraphite, lithium titanate, lithium, a lithium alloy, another activematerial or a combination thereof. Anode form 324 may also includebinder and other inert ingredients. For example, anode 320 may be formedby creating a mixture of active material powder, binder powder, solventand then compressing the mixture over current collector 322 or otherwisecoating current collector 322. Other techniques known to those in theart may also be used to from anode 320.

Cathodes 220A, 220B are positioned adjacent one another in a stackedarrangement to form a cathode stack in the electrochemical cell ofbattery 200. Anodes 320 are positioned on opposite sides of the cathodestack. Locating cathodes 220A, 220B in a stacked arrangement withinbattery 200 may provide one or more advantages when compared to abattery in which does not includes multiple cathodes or in which thecathodes are not located adjacent to each other. As one example, placinganodes on both sides of a cathode stack increases the area of theanode-cathode interface of the battery, thereby lowering the resistanceof the battery.

As another example, during discharge of a battery, such as battery 200,the cathodes may expand in a direction about perpendicular to thethickness dimension of the cathode. For reference, the thickness ofcathode 220B is indicated in FIG. 3A with reference number 227. Theamount of expansion is dependent on the thickness of the cathode, e.g.,thickness 227 of cathode 220B. For example, the expansion may heapproximately equal to the thickness of the cathode. By includingmultiple cathodes in a cathode stack, as with cathodes 220A, 220B inbattery 200, in place of a single, thicker cathode, the cathode stackcan be expect to expand less than the single thicker cathode wouldduring discharge of the battery because each cathode in the cathodestack is thinner than the single thicker cathode having the same totalcharge capacity as the cathode stack would be. Because battery housingdesigns, such as battery housing 200 should account for cathodeexpansion during discharge, limiting the expansion of the cathodes inthe battery by having a cathode stack instead of a single cathode mayallow the cathode stack to more efficiently fill the interior area ofthe battery housing as compared to a battery within a single cathode.This may increase the charge density of the battery.

In another example, having multiple cathodes in a cathode stack insteadof a single cathode may decrease the time need to fill housing 210 withelectrolyte during manufacturing of the battery. For example, housing210 may include one or more fill ports (not shown) used to drawelectrolyte, such as an electrolyte including a lithium salt solution,after assembling the electrode stack, but before sealing housing 210.Because multiple cathodes in a cathode stack have a greater surface areathan a single cathode having the same charge capacity, the electrolytemay permeate the cathodes in a cathode stack faster than it wouldpermeate the single thicker cathode having the same charge capacity ofthe cathode stack. For example, if a battery with the single thickercathode having the same charge capacity of the cathode stack of battery200 takes two minutes to fill with electrolyte during assembly of thebattery, battery 200 may take a minute or less to fill with electrolyte.Also because multiple cathodes in a cathode stack have a greater surfacearea than the single thicker cathode having the same charge capacity,the electrolyte may more completely permeate the cathodes of the cathodestack.

In battery 200, cathodes 220A, 220B are substantially similar. Forexample, the active material of cathode 220A is substantially similar tothe active material of cathode 220B. In addition, cathode 220A has asubstantially similar shape and profile to that of cathode 220B. Inaddition, cathodes 220A, 220B may be considered interchangeable withinbattery 200. However, in other examples of a battery having multiplecathodes in a cathode stack, the cathodes of the cathode stack may bedifferent from each other. For example, one or more cathodes in thecathode stack may facilitate a higher power output whereas one or moreother cathodes in the cathode stack may provide a higher energy density.As another example, the cathodes may have different shapes facilitate anirregularly shaped battery. This may allow for more efficient packing ofcomponents in an electronic device including the battery. This may beparticularly advantageous with respect to IMDs where it is generallydesirable to design an IMD to be as small as possible, e.g., in terms ofvolume, footprint, and/or thickness.

Battery 200 further includes separator 290 positioned between cathodes220 and anodes 320. Separator 290 is a permeable membrane that functionsto keep cathodes 220 and anodes 320 physically separated to prevent anelectrical short circuit. As one example, separator 290 may be a polymerseparator. In the example of battery 200, cathodes 220 are covered byseparator layers 290, which may simplify the construction and assemblyprocess of battery 200. In other examples, separator layers 290 may onlybe placed between adjacent cathodes and anodes.

Feedthrough 212 includes a feedthrough pin 214 that extends throughhousing 210, and an insulator (not shown) separating feedthrough pin 214from housing 210. Feedthrough pin 214 directly connects to currentcollectors 222 of cathodes 220 via electrically conductive tabs 223. Forexample, electrically conductive tabs 223 may include apertures toreceive feedthrough pin 214, and feedthrough pin 214 may be welded toelectrically conductive tabs 223. In this manner, feedthrough pin 214serves as positive terminal for battery 200.

In another example, the cathode stack may include a common currentcollector element folded into a compact configuration, the commoncurrent collector element having a central portion and a plurality oftab portions extending outwardly from the central portion when thecommon current collector element is unfolded, the tabs each having agenerally planar plate portion. Current collectors 222 are included inthe tabs of the common current collector element, such that the commoncurrent collector element provides a direct electrical connectionbetween each cathode 220. The central portion of the common currentcollector element being folded in the compact configuration such thatthe plate portions are positioned to generally overlap each other in thestacked arrangement, and the tab portions being folded in the compactconfiguration such that the stacked plate portions are spaced apart fromeach other in the stacked arrangement of cathodes 220 in the cathodestack. For example, techniques relating to foldable common currentcollector elements are disclosed in U.S. Pat. No. 7,035,078 toViavattine, titled “FOLDED PLATE ELECTRODE ASSEMBLIES FOR BATTERYCATHODES,” the entire content of which is incorporated by referenceherein.

Anodes 320 connect directly to housing 210, via anode collectors 322and/or electrically conductive tabs 323. In this mariner, battery 210represents a case-negative configuration in that housing 210 serves asnegative terminal for battery 200. In other examples, a batteryincluding an electrochemical cell in accordance with the techniquesdisclosed herein may be arranged in a case-positive configuration or acase-neutral configuration. In the example of case neutral, the batterywould include a separate positive and negative battery terminals, andmay include, for example, two feedthroughs, one serving as a positiveterminal and the other serving as a negative terminal for the battery.In any of these examples, the battery may include a liner (not shown)between the electrode stack and the interior of the battery housing toelectrically insulate the anodes and cathodes from each other and fromthe battery housing.

Battery 200 includes one example of an electrochemical cell withadjacent cathodes, but there are many other electrochemical cellsconfigurations including adjacent cathodes in accordance with thetechniques disclosed herein. FIGS. 4-9 illustrate some examples ofelectrochemical cells with adjacent cathodes.

FIG. 4 illustrates electrochemical cell 400. Electrochemical cell 400 isthe same as the electrochemical cell of battery 200. Electrochemicalcell 400 includes cathodes 220A, 220B, which are positioned adjacent oneanother in a stacked arrangement to form a cathode stack. Anodes 320 arepositioned on opposite sides of the cathode stack. Separator 290 ispositioned over cathodes 220, such that separator 290 is positioned notonly between cathodes 220 and anodes 320, but also between cathodes220A, 22B themselves. As previously mentioned, the arrangement ofseparator 290 and cathodes 220 may simplify assembly of a batteryincluding electrochemical cell 400. For example, separator 290 would notneed to be stacked within separately within the battery, and cathodes220A, 220B may be interchangeable.

In other examples, an electrochemical cell may include separator onlybetween a cathode stack and adjacent anodes. One such example isillustrated as electrochemical cell 450 in FIG. 5. Electrochemical cell450 includes cathodes 220A, 220B, which are positioned adjacent oneanother in a stacked arrangement to form a cathode stack. Anodes 320 arepositioned on opposite sides of the cathode stack. Separator 292 ispositioned only between cathodes 220 and anodes 320, but not betweencathodes 220A, 220B themselves. As compared to electrochemical cell 400,electrochemical cell 450 includes two less layers of separator, whichreduces the thickness of electrochemical cell 450 without reducing thecharge capacity electrochemical cell 450. For this reason, theconfiguration of electrochemical cell 450 may be expected to provide ahigher charge density than the configuration of electrochemical cell400.

FIG. 6 illustrates electrochemical cell 500, which represents anotherexample of an electrochemical cell with adjacent cathodes.Electrochemical cell 500 includes cathodes 220A, 22B, which arepositioned adjacent one another in a stacked arrangement to form a firstcathode stack. Electrochemical cell 500 also includes cathodes 220C,220D, which are positioned adjacent one another in a stacked arrangementto form a second cathode stack. Anode 330 is positioned between thefirst and second cathode stack, whereas anodes 320A, 320B are positionedadjacent the first cathode stack and the second cathode stackrespectively and opposite anode 330. Separator 290 is positioned overcathodes 220, such that separator 290 is positioned not only betweencathodes 220 and anodes 320, 330, but also between cathodes 220A, 220Band between 220C, 220D. As previously mentioned, the arrangement ofseparator 290 and cathodes 220 may simplify assembly of a batteryincluding electrochemical cell 500. For example, separator 290 would notneed to be stacked within separately within the battery, and cathodes220A, 220B, 220C, 220D may be interchangeable.

FIG. 7 illustrates electrochemical cell 550, which represents anotherexample of an electrochemical cell with adjacent cathodes.Electrochemical cell 550 includes cathodes 220A, 220B, 220C that arepositioned adjacent one another in a stacked arrangement to form acathode stack. Anodes 320 are positioned on opposite sides of thecathode stack. Separator 290 is positioned over cathodes 220, such thatseparator 290 is positioned not only between cathodes 220 and anodes320, but also between cathodes 220A, 220B, 220C themselves. Aspreviously mentioned, this arrangement may simplify assembly of abattery including electrochemical cell 550. For example, separator 290would not need to be stacked within separately within the battery, andcathodes 220A, 220B, 220C may be interchangeable.

The electrochemical cells of FIGS. 4-7 each include substantiallysimilar cathodes, i.e., cathodes 220. However, in other examples, in anelectrochemical cell including multiple cathodes in a cathode stack, thecathodes of the cathode may not all be substantially similar to eachother. For example, one or more cathodes in the cathode stack mayfacilitate a higher power output whereas one or more other cathodes inthe cathode stack may provide a higher energy density. As anotherexample, the cathodes may have different shapes facilitate anirregularly shaped battery. This may allow for more efficient packing ofcomponents in an electronic device including the battery. This may beparticularly advantageous with respect to IMDs where it is generallydesirable to design an IMD to be as small as possible, e.g., in terms ofvolume, footprint, and/or thickness.

FIG. 8 illustrates electrochemical cell 600, which represents oneexample configuration in which cathodes in a cathode stack are notsubstantially similar to one another. Electrochemical cell 600 includescathodes 220A, 220B, 240, which are positioned adjacent one another in astacked arrangement to form a cathode stack. Cathodes 220 include adifferent active material than cathode 240. For example, the activematerial of cathodes 220 may facilitate a higher power output, whereasthe active material of cathode 240 provides a higher energy density. Forexample, because cathodes 220 are positioned at the anode-cathodeinterfaces within electrochemical cell 600, the power of electrochemicalcell 600 may be increased compared to an electrochemical cell 600including only multiple cathodes 240. However, because the activematerial of cathode 240 provides a higher energy density than that ofcathodes 220, the energy density of electrochemical cell 600 may beincreased compared to an electrochemical cell 600 including onlymultiple cathodes 220.

Anodes 320 are positioned on opposite sides of the cathode stack ofelectrochemical cell 600. Separator 290 is positioned over cathodes 220,240, such that separator 290 is positioned not only between cathodes 220and anodes 320, but also between cathodes 220A, 220B, 240 themselves. Aspreviously mentioned, this arrangement may simplify assembly of abattery including electrochemical cell 600. For example, separator 290would not need to be stacked within separately within the battery.

FIG. 9 illustrates electrochemical cell 650, which represents anotherconfiguration in which cathodes in a cathode stack are not substantiallysimilar to one another. Electrochemical cell 650 includes cathodes 220A,220B, 250, which are positioned adjacent one another in a stackedarrangement to form a cathode stack. As shown in FIG. 9, cathode 250 isthicker than cathodes 220. Due to the different thicknesses of cathodes220, 250, cathodes 220 may facilitate a higher power output, whereascathode 250 may provide a higher energy density than cathodes 220. Forexample, the increased thickness of cathode 250 as compared to cathodes220 allows more active material without any additional current collectormaterial. In this manner, cathode 250 may provide a higher energydensity than cathodes 220. However, the greater surface area of cathodes220 as compared to cathode 250 may allow cathodes 220 to facilitate ahigher power output than in a cathode stack having only thickercathodes.

Anodes 320 are positioned on opposite sides of the cathode stack ofelectrochemical cell 650. Separator 290 is positioned over cathodes 220,250, such that separator 290 is positioned not only between cathodes 220and anodes 320, but also between cathodes 220A, 220B, 250 themselves. Aspreviously mentioned, this arrangement may simplify assembly of abattery including electrochemical cell 650. For example, separator 290would not need to be stacked within separately within the battery.

While the configurations of the electrochemical cells in FIGS. 4-9represent some examples of electrochemical cells with adjacent cathodes,these examples are merely for illustrative purposes and numerous otherexamples exist. For example, the techniques demonstrated withelectrochemical cells in FIGS. 4-9, 12 and 13, as well as the battery ofFIGS. 10A-10B may be combined in any manner to create differentconfigurations of electrochemical cells with adjacent cathodes.

FIGS. 10A-10B illustrate battery 700. More specifically, FIG. 10Aillustrates an exploded view of the components of battery 700, whereasFIG. 10B shows in the components of battery 700 in a full-assembledconfiguration. As one example, battery 700 may be used as battery 106 inIMD (100), although battery 700 may also be used in other applicationssuch as other IMDs or other devices that use batteries. Battery 700includes an electrochemical cell including two anodes 320, 330 and threecathodes 220, 260, 270. Battery 700 further includes two-part housingincluding cup 211A and cover 211B (collectively housing “211”).Feedthrough 212 includes feedthrough pin 214 that passes through housing211 and connects to cathodes 220, 260, 270 to provide a positiveterminal for battery 700.

Battery 700 is substantially similar to battery 200 (FIGS. 3A-3B),except that battery 700 includes anodes and cathodes of varying lengthssuch that battery 700 has a varying thickness. This may allow for moreefficient packing of components in an electronic device includingbattery 700. For example, battery 700 may be designed to fill anirregular available space within an IMD housing or an IMD housing may bedesigned with a more preferable profile, such as a profile with morerounded corners. Because battery 700 is substantially similar to battery200, for brevity features of battery 700 that are the same as orsubstantially similar to features already described with respect tobattery 200, are described with limited or no detail with respect tobattery 700.

Cathodes 220, 260, 270 each include a current collector and a cathodeform of active material covering the current collector. Cathode 260 hasa length shorter than cathode 220 and cathode 270 has a length shorterthan cathode 260 as measured in a direction about perpendicular to thethickness of the cathode stack. Similarly, anode 330 has a lengthshorter than anode 320 as measured in a direction about perpendicular tothe thickness of the cathode stack. The length of anode 330 correspondsto the length of cathode 270, and the length of anode 320 corresponds tothe length of cathode 220. The varying lengths of cathodes 220, 260, 270and anodes 320, 330 allows battery housing 211 to have angled surface215, rather than having a rectangular profile as battery housing 210 ofbattery 200 (FIGS. 3A-3B). Specifically, a thickness of battery housing211 as measured in the direction about perpendicular to the thickness ofthe cathode stack varies to conform to the different lengths of anodes320, 330 and the different lengths of the cathodes 220, 260, 270.

Battery 700 further includes separator 290 positioned between cathodes220, 260, 270 and anodes 320, 330. Separator 290 is a permeable membranethat functions to keep cathodes 220, 260, 270 and anodes 320, 330physically separated to prevent an electrical short circuit. As oneexample, separator 290 may be a polymer separator. In the example ofbattery 700, cathodes 220, 260, 270 are covered by separator layers 290,which may simplify the construction and assembly process of battery 700.In other examples, separator layers 290 may only be placed betweenadjacent cathodes and anodes.

Feedthrough 212 includes a feedthrough pin 214 that extends throughhousing 211, and an insulator (not shown) separating feedthrough pin 214from housing 211. Feedthrough pin 214 directly connects to the currentcollectors of cathodes 220, 260, 270 via electrically conductive tabs ofthe cathodes. For example, the electrically conductive tabs may includeapertures to receive feedthrough pin 214, and feedthrough pin 214 may bewelded to electrically conductive tabs 223. In this manner, feedthroughpin 214 serves as positive terminal for battery 700. Battery 700 alsoincludes metal spacers 280 between the electrically conductive tabs ofthe current collectors of cathodes 220, 260, 270. Metal spacers 280 alsoinclude apertures to receive feedthrough pin 214. In one example, theelectrically conductive tabs of the current collectors of cathodes 220,260, 270 may be first welded to metal spacers 280, and then the entirecathode stack may be positioned such that and feedthrough pin 214extends though all of the electrically conductive tabs of the currentcollectors of cathodes 220, 260, 270 and through metal spacers 280. Thena single weld on the bottom side of the electrically conductive tabs ofthe current collector of cathode 220 may be used to electrically connectthe entire cathode stack to feedthrough pin 214.

Anodes 320 connect directly to housing 211, via anode collectors 322and/or electrically conductive tabs 323. In this manner, battery 211represents a case-negative configuration in that housing 211 serves asnegative terminal for battery 700. In other examples, a batteryincluding an electrochemical cell in accordance with the techniquesdisclosed herein may be arranged in a case-positive configuration or acase-neutral configuration.

FIG. 11 is a flow chart illustrating techniques for manufacturing abattery including an electrochemical cell with adjacent cathodes. Forclarity, the techniques of FIG. 11 are described with respect to battery200 (FIG. 3A-3B).

First, cathode 220A and cathode 220B are manufactured with separatecathode forms 224. In some examples, collector mix including an activecathode material is applied to the current collectors 222 to formcathode 220A and cathode 220B (701). Each current collector 222 may be adistinct component or the current collectors may be part of a foldablecommon current collector element as discussed previously. In someexample, current collectors 222 may be coated with the active cathodematerial to create cathode forms 224. In other examples, the activecathode material may be compressed over current collectors 222 in a moldto create cathode forms 224. Other techniques may also be used to applyactive material to current collectors 222. Then, cathode 220A andcathode 220B are positioned adjacent one another in a stackedarrangement to form a cathode stack. As previously mentioned, cathodes220 each include a current collector 222 and a cathode form 224 ofactive material covering the current collector 222.

Next, anodes 320 are positioned adjacent to the cathode stack thatincludes cathodes 220 (702). Separator 290 is located between thecathode stack and anodes 320. The electrode stack, including the cathodestack of cathodes 220 and anodes 320 is placed within battery housing210. Anode 320A is electrically connected to housing cup 210A, and anode320B is electrically connected to housing cover 210B such that thathousing 210 serves as negative terminal for battery 200. In addition,feedthrough pin 214 of feedthrough 212 directly connects to currentcollectors 222 of cathodes 220 via electrically conductive tabs 223. Forexample, electrically conductive tabs 223 may include apertures toreceive feedthrough pin 214, and feedthrough pin 214 may be welded toelectrically conductive tabs 223. In this manner, feedthrough pin 214serves as positive terminal for battery 200.

Once the electrode stack is positioned within housing cup 210A, cover210B is secured to cup 210A and sealed. For example, housing cover 210Bmay be welded to housing cup 210A. Then housing 210 is filled withelectrolyte via fill port on housing 210 (706). In one example, a vacuummay be applied to a vacuum port on housing 210 while filling housing 210with electrolyte to increase the fill rate of housing 210. Once housing210 is filled with electrolyte, the fill port and the vacuum port (ifany) are sealed (708).

In the examples of batteries 200, 700 and electrochemical cells 400,450, 500, 550, 600, 650, the electrode stacks include anodes outside ofthe cathode stacks. However, as illustrated in FIGS. 12 and 13,electrochemical cells with adjacent cathodes may also be configured suchthat cathodes stacks are outside of the anodes.

Electrochemical cell 800 includes cathodes 220A, 220B, 220C, 220D andanode 330. In the example of electrochemical cell 800, illustrated inFIG. 12, a first cathode stack including cathodes 220A, 220B is locatedon one side of anode 330 and a second cathode stack including cathodes220C, 220D is located on the opposite side of anode 330. Each cathodestack is only adjacent to one anode, whereas anode 330 is adjacent toand between both of the cathode stacks in electrochemical cell 800.

Electrochemical cell 800 further includes separator layers 294, 296positioned between adjacent cathodes 220 and anode 330. Each separatorlayer 294, 296 is a permeable membrane that functions to keep cathodes220 and anode 330 physically separated to prevent an electrical shortcircuit. In different examples, separator layers 294, 296 may be formedfrom different materials or from substantially similar materials. Theuse of the two separator layers 294, 296, i.e., a 2-ply separator,allows further customization of electrochemical cell 800, e.g., to meetdesired performance characteristics, as compared to an electrochemicalcell with single-ply separator layers. As one example, each separatorlayer 294, 296 may be a polymer separator. In the example ofelectrochemical cell 800, anode 330 is covered by separator layers 294,296. In other examples, separator layer 294, 296 may only be placedbetween adjacent cathodes and anodes or may cover one or more ofcathodes 220.

FIG. 13 illustrates electrochemical cell 850, which provides anotherexample of an electrochemical cell configured such that cathodes stacksare outside of the anodes. Electrochemical cell 850 includes cathodes220A, 220B, 220C, 220D, 220E, 220F, 220G, 220H and anodes 330A, 330B.Electrochemical cell 850 comprises a first cathode stack includingcathodes 220A, 220B located on one side of anode 330A and a secondcathode stack including cathodes 220C, 220D, 220E, 220F is located onthe opposite side of anode 330A. The second cathode stack includingcathodes 220C, 220D, 220E, 220F is also adjacent to anode 330B such thatthe second cathode stack is between anodes 330A, 330B. Electrochemicalcell 850 further comprises a third cathode stack including cathodes220G, 220H. The third cathode stack is adjacent to anode 330B such thatanode 330B is between the third cathode stack and the second cathodestack within electrochemical cell 850.

Electrochemical cell 850 further includes separator 294 positionedbetween adjacent cathodes 220 and anodes 330. In the example ofelectrochemical cell 850, anodes 330 are covered by separator layer 294.In other examples, separator 294 may only be placed between adjacentcathodes and anodes or may cover one or more of cathodes 220.

FIG. 14 illustrates an exploded view of another embodiment of anelectrochemical cell 900. Electrochemical cell comprises anode 902 andcathodes 904A-904J. Cathodes 904A-904E and 904F-904J are connectedtogether via current collector connectors 908 to form first cathodestack 906A and second cathode stack 906B.

FIG. 15 illustrates electrochemical cell 950 having first cathode stack906A located on one side of anode 902 and second cathode stack 906Blocated on the opposite side of anode 902. The cathode stacks areseparated from the anode by separator layers 294 which fully cover theanode in this embodiment. The cathodes in each of the cathode stacks areconnected together via current collector connectors 908. The currentcollector connectors 908 are exposed portions of a continuous currentcollector 910A and 910B which are not covered with cathode material,

FIGS. 16 and 17 illustrate another embodiment of an electrochemical cell1000 in cross-sectional and perspective views. Electrochemical cell 1000comprises anode 1010 and cathode stacks 1020A and 1020B adjacent to theanode with separator layers 294 positioned between the anode and theadjacent cathode stacks. In this embodiment, cathode stacks 1020A and1020B are shaped in the form of an oval-shaped coil wherein a continuouslength of cathode material is folded into a stack substantially in theshape of a coil. In this embodiment, each cathode stack 1020A and 1020Bhas cathodes in a stack in the form of cathode layers 1022F-1022J and1022A-1022E, respectively. Cathode stacks 1020 A and 1020B containcurrent collector(s) 1030A and 1030B.

Various examples of this disclosure have been described. However,various modifications to the described examples can be made within thespirit of this disclosure, For example, while the disclosed energystorage techniques were generally described with respect to implantablemedical devices in general and cardiac stimulators in particular, thedisclosed energy storage techniques may be utilized in otherapplications including, for example, other implantable medical devices,such as implantable pumps, neurostimulators or other IMDs. In addition,the disclosed energy storage techniques may also be applied outside themedical field. For example, the disclosed energy storage techniques mayhe used in portable consumer electronics or other areas that utilizeelectrochemical cells. These and other examples are within the scope ofthe following claims.

What is claimed is:
 1. An electrochemical cell comprising: a firstcathode, wherein the first cathode includes a first current collectorand a first cathode form of active material covering the first currentcollector; a second cathode, wherein the second cathode includes asecond current collector and a second cathode form of active materialcovering the second current collector, wherein the second currentcollector is in electrical contact with the first current collector,wherein the first and second cathodes are adjacent one another in astacked arrangement to form a cathode stack in the electrochemical cell;an anode adjacent to the cathode stack; and a separator located betweenthe cathode stack and the anode.
 2. The electrochemical cell of claim 1,wherein the anode is a first anode and the separator is a firstseparator, the electrochemical cell further comprising: a second anodeadjacent to the cathode stack and opposite the first anode relative tothe cathode stack; and a second separator between the cathode stack andthe second anode.
 3. The electrochemical cell of claim 2, furthercomprising a third separator between the first and the second cathode.4. The electrochemical cell of claim 2, wherein the cathode stackfurther includes a third cathode such that the third cathode is adjacentthe second cathode in the cathode stack, wherein the third cathodeincludes a third current collector and a third cathode form of activematerial covering the third current collector, and wherein the thirdcurrent collector is in electrical contact with the first and secondcurrent collector.
 5. The electrochemical cell of claim 2, furthercomprising: a third cathode adjacent to the second anode and oppositethe cathode stack relative to the second anode, wherein the thirdcathode includes a third current collector and a third cathode form ofactive material covering the third current collector, wherein the thirdcurrent collector is in electrical contact with the first and secondcurrent collector; a third separator between the third cathode and thesecond anode; a third anode opposite the second cathode relative to thethird cathode; and a fourth separator between the third cathode and thethird anode.
 6. The electrochemical cell of claim 5, wherein the cathodestack is a first cathode stack, the electrochemical cell furthercomprising: a fourth cathode adjacent to the third cathode such that thethird cathode and the fourth cathode form a second cathode stack in theelectrochemical cell, wherein the fourth cathode includes a fourthcurrent collector and a fourth cathode form of active material coveringthe fourth current collector, wherein the fourth current collector is inelectrical contact with the third current collector.
 7. Theelectrochemical cell of claim 1, wherein the cathode stack is a firstcathode stack and wherein the separator is a first separator, theelectrochemical cell further comprising: a third cathode, wherein thethird cathode includes a third current collector and a third cathodeform of active material covering the third current collector; a fourthcathode, wherein the fourth cathode includes a fourth current collectorand a fourth cathode form of active material covering the fourth currentcollector, wherein the fourth current collector is in electrical contactwith the third current collector, wherein the third and fourth cathodesare adjacent one another in a stacked arrangement to form a secondcathode stack in the electrochemical cell; and a second separatorbetween the anode and the second cathode stack.
 8. The electrochemicalcell of claim 1, wherein the first cathode has a substantially differentactive material than the second cathode such that the second cathode hasa higher energy density than the first cathode.
 9. The electrochemicalcell of claim 1, wherein the second cathode is substantially thickerthan the first cathode as measured in a direction about parallel to thethickness of the cathode stack such that the second cathode has a higherenergy density than the first cathode.
 10. The electrochemical cell ofclaim 1, wherein the first cathode is substantially similar to thesecond cathode.
 11. The electrochemical cell of claim 1, wherein thefirst cathode includes a first electrically conductive tab extendingfrom the first current collector, wherein the second cathode includes asecond electrically conductive tab extending from the second currentcollector, wherein the first electrically conductive tab is inelectrical contact with the second electrically conductive tab.
 12. Theelectrochemical cell of claim 1, wherein the cathode stack includes acommon current collector element folded into a compact configuration,the common current collector element having a central portion and aplurality of tab portions extending outwardly from the central portionwhen the common current collector element is unfolded, the tabs eachhaving a generally planar plate portion, wherein the first currentcollector and the second current collector are included in the tabs ofthe common current collector element, and the central portion beingfolded in the compact configuration such that the plate portions arepositioned to generally overlap each other in the stacked arrangement,and the tab portions being folded in the compact configuration such thatthe stacked plate portions are spaced apart from each other in thestacked arrangement.
 13. A battery comprising a first cathode, whereinthe first cathode includes a first current collector and a first cathodeform of active material covering the first current collector; a secondcathode, wherein the second cathode includes a second current collectorand a second cathode form of active material covering the second currentcollector, wherein the second current collector is in electrical contactwith the first current collector, wherein the first and second cathodesare adjacent one another in a stacked arrangement to form a cathodestack in the battery; an anode adjacent to the cathode stack; aseparator located between the cathode stack and the anode; electrolyte;arid a battery housing that holds the cathode stack, the anode, theseparator, and the electrolyte.
 14. The battery of claim 13, wherein theanode is a first anode and the separator is a first separator, thebattery further comprising: a second anode adjacent to the cathode stackand opposite the first anode relative to the cathode stack; and a secondseparator between the cathode stack and the second anode.
 15. Thebattery of claim 14, wherein the first cathode is adjacent to the firstanode, wherein the second cathode is adjacent to the second anode,wherein the first anode is longer than the second anode as measured in adirection about perpendicular to the thickness of the cathode stack,wherein the first cathode is longer than the second cathode as measuredin the direction about perpendicular to the thickness of the cathodestack, wherein a thickness of the battery housing as measured in thedirection about perpendicular to the thickness of the cathode stackvaries to conform to the different lengths of the first anode and thesecond anode and the different lengths of the first cathode and thesecond cathode.
 16. The battery of claim 13, wherein the first cathodehas a substantially different active material than the second cathodesuch that the second cathode has a higher energy density than the firstcathode.
 17. The battery of claim 13, wherein the second cathode issubstantially thicker than the first cathode as measured in a directionabout parallel to the thickness of the cathode stack such that thesecond cathode has a higher energy density than the first cathode. 18.The battery of claim 13, wherein the first cathode is substantiallysimilar to the second cathode.
 19. The battery of claim 13, wherein thecathode stack includes a common current collector element folded into acompact configuration, the common current collector element having acentral portion and a plurality of tab portions extending outwardly fromthe central portion when the common current collector element isunfolded, the tabs each having a generally planar plate portion, whereinthe first current collector and the second current collector areincluded in the tabs of the common current collector element, and thecentral portion being folded in the compact configuration such that theplate portions are positioned to generally overlap each other in thestacked arrangement, and the tab portions being folded in the compactconfiguration such that the stacked plate portions are spaced apart fromeach other in the stacked arrangement.
 20. A method of manufacturecomprising: positioning a first cathode and a second cathode adjacentone another in a stacked arrangement to form a cathode stack, whereinthe first cathode includes a first current collector and a first cathodeform of active material covering the first current collector, whereinthe second cathode includes a second current collector and a secondcathode form of active material covering the second current collector;positioning an anode adjacent to the cathode stack with a separatorlocated between the cathode stack and the anode; and electricallyconnecting the first current collector and the second current collector.21. The method of claim 20, farther comprising: locating, the anode, theseparator and the cathode stack within a battery housing with the anodeadjacent to the cathode stack and with the separator located between thecathode stack and the anode; and filling the battery housing withelectrolyte.
 22. The method of claim 20, further comprising electricallyconnecting the first current collector and the second current collectorto a feedthrough pin that extends through the battery housing to form apositive battery terminal.
 23. The method of claim 22, wherein thebattery housing is electrically connected to the anode such that thebattery housing serves as a negative battery terminal.
 24. Animplantable medical device comprising: a hermetically sealed housing;and a battery disposed within the housing for powering the implantablemedical device, the battery comprising: a first cathode, wherein thefirst cathode includes a first current collector and a first cathodeform of active material covering the first current collector; a secondcathode, wherein the second cathode includes a second current collectorand a second cathode form of active material covering the second currentcollector, wherein the second current collector is in electrical contactwith the first current collector, wherein the first and second cathodesare adjacent one another in a stacked arrangement to form a cathodestack in the battery; an anode adjacent to the cathode stack; aseparator located between the cathode stack and the anode; electrolyte;and a battery housing that holds the cathode stack, the anode, theseparator, and the electrolyte.
 25. The implantable medical device ofclaim 24, further comprising a control module within the hermeticallysealed housing, wherein the control module controls electricalstimulation functions of the implantable medical device.
 26. Theimplantable medical device of claim 25, wherein the implantable medicaldevice is a cardiac stimulator.